ph4nt0m wrote:There's one thing about 256K PPro's. While the core is 350nm indeed, the cache die is still 600nm. So it may be a limiting factor. Many 256K PPro's don't even POST at 266MHz, though 1M chips don't do it either. The 512K PPro comes with a single 350nm cache die. It takes two of these for the 1M chip with a lot of power consumption. I have measured 11.7A @ 233MHz on the VRM while running Memtest.

I have recently overclocked one 200MHz/256K to 266MHz at 3.4V. It was unstable in benchmarks and couldn't compile a damn thing, so I modded it by soldering 10 1.0uF capacitors on the top.

It's fine now, passes all benchmarks and can compile a Linux kernel. What's really interesting, this is an early SY013 with the A0 core revision and A cache revision. It isn't supposed to do 266MHz, but it does.

That's an awesome mod!

Only PPro machine that I saw in real life was back in '99 at a friends house - 24" CRT included.

The machine was a few years old and he must have spent a fortune on it. He wanted to sell it to me for a few hundred and I refused as I had no use for it.

For those who are considering this mod for themselves, a great source of such 1.0uF capacitors is Socket 370 Coppermine chips whether Pentium 3 or Celeron. These are very inexpensive especially if broken because gold refiners don't want them usually. It's much more expensive to buy new capacitors from distributors. A set of 10 costs $5 to $10 there.

ph4nt0m wrote:For those who are considering this mod for themselves, a great source of such 1.0uF capacitors is Socket 370 Coppermine chips whether Pentium 3 or Celeron. These are very inexpensive especially if broken because gold refiners don't want them usually. It's much more expensive to buy new capacitors from distributors. A set of 10 costs $5 to $10 there.

What is this mod actually? Why the CPU will run faster if those capacitors are soldered?

ph4nt0m wrote:For those who are considering this mod for themselves, a great source of such 1.0uF capacitors is Socket 370 Coppermine chips whether Pentium 3 or Celeron. These are very inexpensive especially if broken because gold refiners don't want them usually. It's much more expensive to buy new capacitors from distributors. A set of 10 costs $5 to $10 there.

What is this mod actually? Why the CPU will run faster if those capacitors are soldered?

Because low ESR/ESL bypass capacitors are very important in high frequency designs. There are bulk electrolytic capacitors in the VRM, some tantalum and/or ceramic capacitors near the CPU socket, but none on the CPU itself. Internal CPU power traces, socket pins and mainboard power traces introduce a lot of impedance. So what seems to be a quality power supply isn't actually at the point of load.